Quote from Dr. Garrett Smith on December 24, 2018, 1:58 pm

Long term vitamin A restriction improves meat quality parameters and modifies gene expression in Iberian pigs.

[...] Results found in this experiment show that long-term restriction of dietary vitamin A has a positive effect on nutritional and sensorial parameters of ham meat. Moreover, gene expression results were consistent with the vitamin A transcriptional regulation of adipogenesis and lipogenesis and with the changes observed in meat and fat composition.

Another study that shows that pigs did just fine without supplementing their diet with any Vitamin A:

Dietary vitamin A restriction affects adipocyte differentiation and fatty acid composition of intramuscular fat in Iberian pigs.

Decreasing added vitamin A in feed from two to four months of age caused an increase in the number of preadipocytes and suggestive downregulates the CRABPII [cellular retinoic acid binding protein 2] gene. In addition, vitamin A restriction for 9 months caused a pronounced increase of total NL, monounsaturated fatty acids and a decrease of saturated fatty acids in NL [neutral lipids] fraction of IMF [intramuscular fat]. This change in fatty acids profile has a positive effect on costumer's [sic] health.

This approach is an easy and no cost-increasing strategy to increase the lipid content in muscle of Iberian pigs with no detrimental effects on carcass traits. The greater lipid content would lead to an increase in meat quality, which is highly appreciated in meat products obtained from this breed. However, further studies on different added dietary vitamin A level (0, NRC recommended levels, commercial levels) would improve the knowledge about this topic.

Restricting Poison/"Vitamin A" in the first 2-4 months of life caused NO problems.
Restricting Poison/"Vitamin A" for 9 months caused NO problems.
Restricting Poison/"Vitamin A" increased the meat quality.

IF this so-called "essential" nutrient is critically important in proper development--and causes major developmental and health issues if it is missing from the diet--how can the above things be true?  The answer is, it is NOT an essential vitamin and it is actually a POISON/TOXIN.  Only one can be true.

And another one, showing that pigs "restricted" from extra Poison/"Vitamin A" for most of their lives ended up needing less food and less Vitamin E, resulting in cost savings to the farmers who follow the science:

Effects of dietary vitamin A supplementation or restriction and its timing on retinol and α-tocopherol accumulation and gene expression in heavy pigs

Vitamin supplementation is a widely extended practice in swine nutrition. Certain vitamins such as vitamins A and E are related to meat quality and have been reported as antagonists. Thus, their tissue levels are of interest for swine producers and consumers. This experiment was undertaken to study the effect of dietary vitamin A supplementation or withdrawal duration and timing on the evolution of vitamin A deposition in tissues, α-tocopherol accumulation and gene expression in heavy pigs. Eighty weaned Iberian piglets (16.3 ± 2.5 kg) were either fed a vitamin A-enriched diet (10,000 IU vitamin A/kg) (CONTROL) or given a diet without added vitamin A applied from the beginning of the trial at 16.3 kg (early restriction group, ER) or from an average weight of 35.8 kg (late restriction group, LR). Pigs fed ER and LR had lower ADG and worse feed efficiency than those from the CONTROL group at 101.4 kg (P=0.001 and P=0.034, respectively). However, final weight, average daily gain, average daily intake and feed conversion efficiency were not statistically affected by dietary treatment during the starter (<35.8 kg), fattening period (101.4–157.9 kg) or overall (16.3–157.9 kg). Retinol concentration in tissues reflected the dietary vitamin A level. Retinol and retinyl palmitate accumulation in hepatic and fat depots of control animals was more marked during the growing than during the finishing period. Retinol depots decreased in restricted groups and showed different sensitivity for mobilization between tissues, with faster retinol mobilization from the liver. The ER group had a higher hepatic α-tocopherol increase than the LR group (P<0.0001). However, in fat the increase in α-tocopherol levels were more marked in the LR than in the ER group (P<0.0001). ADH1C gene expression was higher (P=0.0237) in CONTROL than in ER at 101 kg and LRAT gene expression showed a dose-dependent decrease in the ER group at 101 and 158 kg LW (P<0.0001). There were no differences in RBP4, ALDH1A1, MTTP and TTP gene expression as affected by dietary treatment. Growth time influenced gene expression, with ADH1C and RBP4 genes being mainly expressed at 101 kg LW compared to pigs at 36 or 158 kg LW (P<0.05). Relative expression of MTTP and TTP was also affected by time and showed an opposite pattern to that observed for vitamin A-related genes. The results suggest that removing vitamin A from the diet for long or short periods in heavy pigs has the potential to reduce feed costs, increasing tissue α-tocopherol levels without affecting slaughter weight or feed efficiency.